While polyethylene is widely used in consumer products, its use in other applications is limited because of low adhesive properties. In this study, the adhesive properties of high-density polyethylene were improved by a facile chemical treatment which was no require the special equipment or reagents. This simple treatment enabled the homogeneous modification of a polyethylene surface by dipping in a dilute solution containing a side-chain crystalline block copolymer (SCCBC) for a short time. SCCBC comprises of a block copolymer with one monomer containing long alkane side chains that form the side-chain crystalline units and the other that contains functional monomers. The adhesive strength of the high-density polyethylene film modified by SCCBC, as determined using a T-peel test and tensile shear test, was stronger than the non-modified high-density polyethylene substrate. Furthermore, this facile method imparted these strong adhesive properties to high-density polyethylene over a wide variety of treatment conditions such as temperature of SCCBC solution, concentration, dipping time and types of solvent.